1. Technical Field
The present disclosure relates to an information recording method, an information recording device, and an information recording medium that enable recording of data on the information recording medium having an information recording surface capable of optically recording information on each of lands and grooves.
2. Description of the Related Art
Currently, as an information recording medium that stores video, data, and the like, many types of optical discs are used, such as a digital versatile disk (DVD) and Blu-ray (registered trademark) disc (hereinafter referred to as BD). Since these optical discs have high storage reliability compared with a hard disk drive (hereinafter referred to as a HDD) and a magnetic tape, applications are expanding from conventional recording applications of audiovisual (AV) data, such as video and voice, to prolonged storage of data, that is, applications for archiving data.
However, an optical disc has only about ⅓ of data storage capacity per volume compared with a HDD or magnetic tape. From a viewpoint of space efficiency during storage, development of a technology is desired that increases data storage capacity per volume without increasing cost of a disc, and energetic research and development has been continued.
Recently, a BDXL with a recording density of about 33.4 GB per layer, which has high recording density among BDs, has been on the market as an optical disc with the highest recording density per volume. These optical discs have storage reliability of 50 years or more, and have reliability of 10 times or more compared with about five years of life of a HDD from a viewpoint of long-term storage of data. Accordingly, it is possible to achieve both long-term storage reliability and low storage cost by moving data for long-term storage currently stored in a HDD to an optical disc for storage.
Moreover, from a viewpoint of power consumption, compared with a HDD that consumes electric power during data storage, an optical disc does not need electric power during storage, and can reduce CO2 emissions as a green storage that gives consideration to global environment. Furthermore, in recent years, increase in power consumption in large-scale IT systems, such as a data center, has been a large problem; however, using an optical disc for archive applications allows reduction in power consumption.
For this purpose, in order to use an optical disc for archive applications, because of high cost reduction requirement for storage space such as a data center, improvement in recording density per volume is needed.
Technologies for improving recording density per volume of an optical disc include a land-groove recording-reproduction technology capable of improving recording density of a track, and a technology to narrow a track pitch, which is spacing between tracks.
The land-groove recording-reproduction technology is a technology used in DVD-RAMs. This is a technology to improve recording density of a track by recording data of an optical disc, which is currently recorded only on grooves or only on lands, on both grooves and lands. Usually, improvement in recording density of a track of an optical disc causes weaker diffracted light from grooves needed for performing trace control of grooves, which are tracks, with a light beam, disabling the light beam from tracing a track. When a wavelength of a laser beam used for the light beam with which the optical disc is irradiated is λ and a numerical aperture of a lens that forms the light beam is NA, limit spacing of grooves or lands, that is, limit track pitch L is as follows.L=(λ/NA)×0.6The track pitch smaller than the limit track pitch L disables detection of diffracted light from grooves and disables control to trace the track. For example, in a DVD of NA=0.6 and λ=650 nm, the limit track pitch L is 650 nm. A DVD-RAM achieves 615-nm track pitch and improves the track density by recording data on both lands and grooves (for example, refer to Unexamined Japanese Patent Publication No. H07-029185).
In addition, the technology to narrow the track pitch has also been employed during technical evolution from DVD to BD. In addition to 50% or more reduction of the track pitch from 0.74 μm for DVD to 0.32 μm for BD, further reduction of the wavelength of the laser beam and reduction of a size of a pit, which is a hole made on a recording surface, improves storage capacity from 4.7 GB for DVD to 25 GB or more for BD (for example, refer to “The Strategy of Panasonic for Blu-ray Disc”, Nikkei Business Publications, Inc., 2006, page 30, chart 2-2).
Technology development is currently under way to improve the recording density per volume in an optical disc by further making the track pitch narrower than in BD or BDXL and by recording data on both lands and grooves. This technology development is expected to implement one optical disc with a capacity of 50 GB or more per layer on one side, and a capacity exceeding 150 GB in three layers on one side.
Generally, it is known that recording conditions of adjacent tracks have an influence on a tracking error (TE) signal and the like as the track pitch of an optical disc is reduced. Accordingly, when both lands and grooves of an optical disc are used for recording and the track pitch is reduced, the influence on the TE signal and the like further increases, which has an adverse influence on trace control of a track, recording quality, and the like.
FIG. 19A is a diagram illustrating change in an offset amount of the TE signal at an unrecorded-unrecorded boundary position during trace control of a track in a conventional optical disc that makes recording on grooves and lands of the optical disc. FIG. 19B is a diagram illustrating change in the offset amount of the TE signal at a recorded-unrecorded boundary position during trace control of a track in a conventional optical disc that makes recording on grooves and lands of the optical disc. In FIG. 19A, symmetric amplitude of a waveform of the TE signal is obtained at boundary position 1403 with adjacent unrecorded-unrecorded tracks 1401, 1402. In contrast, in FIG. 19B, the amplitude of the waveform of the TE signal obtained at boundary position 1406 with adjacent recorded-unrecorded tracks 1404, 1405 has significantly collapsed symmetry with changed TE offset amount. This means that, when the recording conditions of adjacent tracks differ from each other, symmetry of amplitude of the TE signal collapses.
When recording is made in a track of an optical disc in such a state, trace control of the track cannot be made optimally, the light beam cannot be applied to an optimal position, and recording quality may be significantly reduced to an unreproducible level. Furthermore, in a worst case, trace control of the track cannot be made at all, causing track jump or the like, which may ruin or crush data recorded on surrounding tracks. Although an optical disc allegedly has storage reliability of 50 years or more, it is apparent that a storage that fails to store data correctly cannot be used for applications including a data center.